The present invention relates to a method for fixing a tube by expansion. Expansion tube fixing is a well known process for joining tubes to support plates. In this fixing process, a bore is formed in a plate, and the end of the tube engages the bore. The outside wall of the tube is then expanded against the inside surface of the bore in the plate by means of a tube expander comprising a plurality of rollers disposed about a tapered spindle.
It is preferred in processes for fixing a tube by expansion that grooves be machined in the inside surface of the bore to improve the connection between the tube and the plate. The grooves are usually 0.5 millimeter (mm) in depth and a few millimeters in width. This grooving process, however, can be used only for fixing thick tubes; because thin tubes, which can be less than one millimeter in thickness, have a tendency to split at the edges of the grooves. Moreover, although the grooving operation improves the interengagement between the tube and the plate, the seal thereof remains virtually unaltered.
It has also been proposed, for fixing thin tubes by an expansion process, for the inside surface of the bore to have machined therein, grooves which are smaller in depth, being for example on the order of three tenths of a millimeter in depth, and with an axial extension (or width) of the same order, that is to say, much less than the grooves used for expansion fixing of thick tubes. When the tube is expanded within the bore, a bead or fillet of metal is formed in the grooves.
This bead improves the seal between the plate and the bore. The technique described, however, has the disadvantage that the operation of machining the grooves is delicate and expensive. In addition, the engagement of the tube in the plate is such that no sliding motion is permitted. This can result in high levels of axial compression stresses in the tube if the tube is also fixed by expansion at its other end.
The present invention eliminates these disadvantages by providing an expansion-fixing method which can be used specifically for the expansion-fixing of thin tubes. The invention improves the seal between the joined components and can be performed in a simple and inexpensive manner.